In the
Dog-days, the frost is so intense that a small icicle becomes in one day
a huge mass of ice; but a cool day promptly brings a thaw, and the cave
is looked upon as a barometer, not merely feeling, but also presaging,
the changes of weather. The people of the neighbourhood, when employed
in field-work, arrange their labour so that the mid-day meal may be
taken near the cave, when they either ice the water they have brought
with them, or drink the melted ice, which they consider very good for
the stomach. It had been calculated that 600 weekly carts would not be
sufficient to keep the cavern free from ice. The ground above the cave
is peculiarly rich in grass.
In explanation of these phenomena, Bell threw out the following
suggestions, which need no comment. The earth being of itself cold and
damp, the external heat of the atmosphere, by partially penetrating into
the ground, drives in this native cold to the inner parts of the earth,
and makes the cold there more dense. On the other hand, when the
external air is cold, it draws forth towards the surface the heat there
may be in the inner part of the earth, and thus makes caverns warm.
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